Porous material and its preparation

ABSTRACT

A porous polymeric material has cell sizes within the range 100 to 0.5 μm and total pore volume with respect to the overall volume of the material in the range 75 to 98% and includes cross-linked polycondensation polymeric material. The material can be made from a high internal phase emulsion in which the cross-linked polycondensation polymer is formed in the continuous phase. The materials are preferably open interconnected cellular structures. They can be made of a wide range of polycondensation materials. The materials are thus highly porous and light weight and have a range of properties depending primarily on their constituent polycondensation materials.

The present invention relates to a porous material and to a process forits preparation. In particular the present invention relates to a porousmaterial whose total pore volume with respect to the overall volume ofthe material is within the range 75 to 98% and to a process involvingthe preparation of a high internal phase emulsion.

It has previously been proposed in U.S. Pat. No. 4,039,489 to preparerelatively low density oil absorbent polymeric materials in the form ofpolystyrene and polyurethane foams using various foaming agents. InBritish Patent No. 1,291,649 proposals have been made to prepare arelatively low density, oil absorbent, polymeric foam by the inclusionof a volatile material into a pre-polymer and then rapidly reducingpressure and permitting the volatile material to expand the polymericmaterial to generate the foam.

In U.S. Pat. No. 3,988,508 Lissant has disclosed the production ofpolymeric materials by polymerization of an oil-in-water emulsion systemhaving a high internal phase ratio of monomer to water, preferably85-95%, although the disclosure is of monomer water ratios in the range20:80 to 95:5 without a cross-linking agent.

The study of high internal phase emulsions has been carried out for manyyears and the basic theory behind their preparation and structure hasbeen discussed by K. J. Lissant in "Surfactant Science Series", Volume6, "Emulsion and Emulsion Technology", Part 1, edited by K. J. Lissant,Marcel Dekker Inc., New York, 1974. In this work Lissant discusses thegeometrical packing of droplets in high internal phase emulsions andsuggests that especial care must be exercised in selecting emulsifyingagents for such compositions and that, in the region of 94-97% volumepercentage of internal phase, critical changes occur in the highinternal phase emulsion (HIPE). Beerbower, Nixon, Philippoff and Wallaceof Esso Research and Engineering Company have studied high internalphase emulsions as safety fuels, such compositions containing at least97% by weight of hydrocarbon fuel (ref. American Chemicals Society,Petro-chemical Pre-prints, 14, 79-59, 1969).

In U.S. Pat. No. 3,255,127, polymeric materials are disclosed which areprepared by polymerization in reversed emulsion. In this specification arelatively small proportion of water is emulsified into a mixture ofemulsifier, catalyst and monomer and the emulsion so produced is mixedinto a far larger proportion of water, usually containing a stabilizersuch as polyvinyl alcohol, which keeps the droplets of reversed emulsionin a relatively stable form. Polymerization takes place in a period ofthe order of 24 hours at 55° C. to yield particulate polymer or polymerblock which can readily be broken down to give a particulate polymer.

In British Patent No. 1,576,228 AKZO disclosed the production ofthermoplastic microporous cellular structures comprising microcellshaving an average diameter of 0.5-100 microns with smaller diameterpores connecting the microcells. These structures are made by dissolvinga suitable thermoplastic polymer in a solvent at elevated temperatureand then cooling the solution to solidify the polymer and then removingthe liquid from the thermoplastic polymer structure. This process isclearly limited in its application to polymers which can readily bedissolved in appropriate solvents.

In British Patent No. 1,513,939, Ceskoslovenska Akademie Ved alsodisclosed the production of porous polymers, but these are formed asporous beads which may be coalesced to form a moulding which willclearly not be homogeneous or uniform in its porosity. The porous beadsare prepared by dissolving the polymer to be used in a solvent and thendispersing the solution into a compatible carrier liquid and thismixture is added to a coagulating liquid such as water to precipitatethe porous beads of polymer. This process is also limited in that ifcross-linked polymers are desired they can only be produced by a randomlinking of pre-formed linear polymer chains.

British Specification No. 2,000,150 discloses the production and use ofcross-linked polymeric porous beads. The beads may be used to extractcomponents from liquid mixtures and typically have a pore volume of 2.42ml/g and are hard enough to be packed into absorbency columns.

British Specification No. 1,458,203 suggests the preparation of shapedcellular articles by curing an emulsion containing up to 90 parts byweight of water to 10 parts by weight of polymerizable mixture.

In British Patent No. 1,428,125, ICI commented on the desirability ofmaximizing the water content of water extended polymers, but theysuggest that difficulty was experienced in obtaining water-in-oilemulsions with water contents in excess of 88% by weight water.

Our earlier EP patent specification No. 0060138 suggests the preparationof a porous homogeneous material from a high internal phase emulsionusing a cross-linked vinyl polymer material.

It is an object of the present invention to provide a novel highlyporous polymeric material. It is a further object of the presentinvention to provide a novel highly porous polymeric material that canbe made by a process that can be readily adapted to continuous orsemi-continuous production methods.

According to a first aspect of the present invention there is provided aporous cross-linked polymeric material having cell sizes within therange 100 to 0.5 μm and total pore volume with respect to that of theoverall volume of the material in the range 75 to 98% wherein thepolymeric material includes cross-linked polycondensation polymericmaterial.

Thus the present invention provides a highly porous cross-linkedpolycondensation material having cell sizes within the range 100 to 0.5μm. The present materials thus differ from conventional foamed forexample polyurethane materials whose cell volumes range from a minimumof about 200 μm to a selected higher value for example 500 μm. Thepresent cross-linked materials also differ significantly from thosedisclosed in GB No. 1576228 which by necessity are thermoplastic andnon-crosslinked.

The present materials preferably have a total pore volume with respectto that of the overall volume of the material of at least 85%, morepreferably of at least 90%.

The present materials preferably comprise a structure of interconnectingcells. The material can thus be very light and can for example have anoverall density of less than 0.25 g/cm³. A realistic minimum overalldensity for a material of 98% overall porosity will be of the order of0.02 g/cm³.

In principle there is no inherent restriction on the polycondensationpolymer comprising the present materials. The polycondensation polymercan thus be chosen from a wide range of materials. For example thepolycondensation polymer can give either a hydrophilic or a hydrophobiccharacteristic to the porous polymeric material, and if desired,functional groups can be present in the polycondensation polymericmaterial.

The present polymeric materials can thus have a high porosity andpermeability in combination with a resistance to chemical attack anddissolution due to their cross-linked nature, the degree ofcross-linking being at least such that the materials retain an integralthree-dimensional matrix even in a solvent swollen state. A range ofmechanical characteristics e.g. tensile strengths, and thermal stabilitycan moreover be imparted to the material, depending primarily on theparticular polycondensation material selected. Such a combination ofproperties at a cell size of 0.5 to 100 μm provides a novel material forwhich many advantageous uses can be envisaged.

Examples of such uses include use as a filter body in a wide variety ofenvironments, use as a carrier for example for a range of catalysts in awide variety of physical and chemical environments, and use as acontainment system for example a range of toxic materials in liquidform. For use as a containment system the present porous materials caneither be prepared having open interconnected cells allowing the toxicor other liquid to be absorbed to provide a non-spill container or,alternatively, the porous materials can be prepared having a closed cellsystem with the toxic or other liquid comprising the dispersed internalphase and thus being immediately contained within the porous polymericmaterial as it is formed providing a non-spill and non-evaporatingcontainment system.

The present materials can moreover be substantially homogeneous and canbe present in a monolithic block form, particulate form or for instancean extruded sheet or strand form. The integral nature of the materialagain allows a wide variety of uses for the material to be contemplated.

The polycondensation polymeric material can be derived from a monomerand/or pre-polymer or mixtures thereof having at least two differentreactive groups. In other words the polycondensation species formed canbe of the type --(X--Y)_(n) -- in which X and Y are derived from thereactive groups. Alternatively the polycondensation polymeric materialcan be derived from at least two types of monomers or pre-polymers. Inother words the polycondensation species formed is of the type --(--X--X--Y--Y--)_(n) -- in which X and Y are derived from the respectivereactive groups on two types of monomer or pre-polymer X'--X' andY'--Y'. In some cases the polymeric material can be formed byring-opening reactions of cyclic molecules e.g. of the type ##STR1## Bypre-polymer we mean a pre-polymerized group of monomers which can bechain extended by a polycondensation reaction to form thepolycondensation polymeric material. Cross-linking is inherent due tothe number of reactive groups on the monomer or prepolymer or can beintroduced by appropriate cross-linking agents. The monomers and/orpre-polymers can be branched and/or straight chain.

Chain-extension or cross-linking can occur by the addition of otherreactive components. For example, poly-condensation cross-linking canoccur by the addition of formaldehyde to a pre-polymer or polymer suchas formed from phenol formaldehyde. Generally the pre-polymers employedwill have a molecular weight within the range 200 to 100,000 and/orchain length of 2 to 1,000 units, preferably 200 to 20,000 molecularweight and/or chain length of 2 to 200 units.

A great variety of polymers can be produced by the present process.Suitable polycondensation reactions are exemplified by the descriptionsin "Condensation Polymers" P. W. Morgan Interscience New York 1965. Thepresent polymers are suitably derived from synthetic materials,particularly those obtained from fossil sources e.g. coal orpetrochemical sources or inorganic sources. The present polymers canhowever be derived from materials derived from natural sources, whichcan if desired by modified e.g. cellulose acetate. Mixtures of sourcescan be employed.

Particular examples of polycondensation polymeric materials which can beemployed in the present invention include the polycondensation productsbetween urea and aldehydes, the polycondensation products betweenphenols and aldehydes, the polycondensation products between resorcinolsand aldehydes, polyvinyl formals, polyesters, polyamides, polyacetals,polyurethanes, polysiloxanes, polyimides, polybenzimidazoles,polyethers, polythioethers, polyketals, polyether sulphones andpolyether ketones and mixtures thereof.

The present polymeric materials can have an overall density of less than0.25 g/cm³. A minimum overall density will be of the order of 0.02g/cm³. These figures as well as those relating to cell size and porevolume relate to the initially formed polymeric material. On washing anddrying, the material may collapse resulting in a change in poredimensions. On placing in a solvent the material may swell, againresulting in a change of pore dimensions.

Preferably, the cell sizes can be within the range of 50 to 5 μm, morepreferably 20 to 0.5 μm, even more preferably 10 to 0.5 μm. The cellsizes can be uniform and readily be of the order of 3.5 μm. Althoughsome few cells may be present with a size below 0.5 μm, the vastmajority will have diameters within the range 100 to 0.5 μm. Preferablythe cells are interconnected by a plurality of holes in the walls of thepores. The holes can be of the order of 8 to 16 per cell or the numberof holes per cell can be very much greater. The holes can be of a sizein the range of 0.2 to 0.05 cell diameter.

The present invention can thus provide a highly porous, adsorbent, andlight-weight material. The materials can be generally homogeneous.Materials can be formed having a dry density of less than 0.25 g/cm³,even less than 0.1 g/cm³, a pore volume of more than 3 cm³ /g and anadsorbency for liquids defined in terms of oleic acid of at least 2.5cm³ /g.

According to a second aspect of the present invention there is provideda process for preparing a porous polymeric material comprising preparingan emulsion whose internal phase comprises 75 to 98 volume % of thematerial and consists of globules having dimensions in the range 100 to0.5 μm and forming in the continuous phase a cross-linkedpolycondensation polymer.

Preferably the internal phase is removed e.g. by washing and drying, thelatter if necessary vacuum assisted.

The formation of the polycondensation polymer can occur spontaneously orcan suitably be initiated by the addition of an acid or base, asappropriate, and/or by heating the emulsion. Polycondensation reactionscan be relatively fast. Cooling can be employed to control the reactionrate.

In one embodiment it is therefore necessary to form the emulsion firsthaving its internal phase of the desired dimensions and then for exampleto stir acid or base into the emulsion and, if necessary, heat.

In another embodiment when the reaction is sufficiently slow theemulsion can be formed containing all the necessary components and thereaction allowed to proceed, if necessary by heating.

In another embodiment the already formed emulsion containing a reactantin the continuous phase, and if necessary an acid or base as catalyst,can be brought into contact with the other reactant which then diffusesinto the continuous phase and interacts with the first reactant to formthe cross-linked polycondensation polymeric material. Suitably the otherreactant is dissolved in an inert solvent and the prepared emulsion isadded to or extruded in sheet like form into the solution. Alternativelythe other reactant could be in gaseous form.

Where two or more reactants are present in the ready formed emulsionthey can each be in the continuous phase, or possibly they can be splitbetween the two phases. In the latter case one or more reactants can beinitially dissolved in one phase and other reactant in the other phaseprior to preparing the emulsion.

Cross-linking is present in the final product either inherently due tothe number of reactive groups on the monomer or prepolymer or by thepresence of appropriate cross-linking agents, for examplepolycondensation cross-linking agents.

In order to prepare the emulsion generally an emulsifier can be present,suitably in a concentration in the range 0.1 to 25% by weight withrespect to the continuous phase. Suitable emulsifiers include amphotericemulsifiers such as Miranol C2M-SF and Admol Wol, Span 80, Tween 20,sucrose esters, and mono-oleate type emulsifiers. Either in the presenceor absence of emulsifiers the emulsion having appropriate size of itsinternal phase can be achieved by stirring using for example aconventional paddle stirrer.

The reactants are suitably present in the emulsion at a concentration of2 to 100 wt % with respect to the continuous phase. The emulsion phasescan be derived from any two immiscible materials. The only requirementis that the phase or phases carrying the reactant materials are able todissolve or disperse the reactant materials in question. The continuousphase can for example be water or an organic solvent such as for examplea hydrocarbon or a chlorocarbon. Alternatively the continuous phase canconsist of one or more of the initial reactants.

The present process can be employed to prepare the present polymericproducts. The reaction times can be nearly instantaneous from forexample the point of the addition of the catalyst or the contacting ofspontaneously reactive components. In practice a minimum reaction timeof about 5 minutes has proved practical with a maximum time being about6 hours. In some instances somewhat longer times may be required.Nonetheless it can be seen that the present process can lend itself toproduction on a continuous or semi-continuous process. It can moreoverbe adept at allowing homogeneous products to be produced in a widevariety of shapes or sizes. The products can for example be formed inintegral blocks in moulds or in sheet, strand or granule form byextrusion. Particulate material can be formed by granulating for exampleblocks of the material.

Appropriate starting materials for the present process are thosedescribed above. Similarly the preferred process conditions are those toprovide the preferred materials mentioned above. For example processconditions preferably include an internal phase of at least 85% byvolume, more preferably at least 90% by volume, and having globuledimensions within the range 20 to 0.5 μm, more preferably 10 to 0.5 μm.

The present invention can thus provide a highly porous cross-linkedpolycondensation material having cell sizes within the 100 to 0.5 μmwhich is made from a high internal phase emulsion.

Embodiments of the present invention will now be described by way ofexample only with reference to the following Examples.

EXAMPLE 1

Resorcinol (8.3 g; 0.075 mol) and formalin (40% aq; 12.2 g; 0.15 molformaldehyde) were added to a polyethylene jar and heated to 30° C. toform a homogeneous solution. After cooling to room temperature anamphoteric emulsifier, MIRANOL C2M-SF. CONC (37% aq; 2.3 g) was added.The resulting clear solution was stirred with a paddle stirrer whilecyclohexane (180 ml) was added dropwise over a period of 30 minutes toform a thick high internal phase emulsion. An acidic catalyst,phosphoric acid (50% aq; 3.0 g) was then stirred into the emulsion. Anopaque rigid polymer was formed after heating at 60° C. for ten minutes.The water and cyclohexane were removed at 75° C. in a vacuum oven.

The resulting porous polymeric material was tough, hydrophobic andsalmon pink in colour. Examination of the material by scanning electronmicroscopy showed it to have a structure comprising a matrix ofinterconnecting cells having diameters within the range 1 to 15 μm. Thematerial had an overall porosity of 90% by volume, a density of about0.1 gcm⁻³, a compressive strength of about 9×10⁵ Nm⁻² and a permeabilityof about 0.1 Darcys.

EXAMPLE 2

The same procedure was used as described in Example 1. 3.0 g ofresorcinol and 4.1 g of formalin were employed. The emulsifier washexadecylpropyl sulphobetaine (nC₁₆ H₃₃ N⁺ (CH₃)₂ (CH₂)₃ SO₃ ⁻) (0.14 g)and the emulsion dispersed phase was heptane (100 ml). Addition of thecatalyst p-toluenesulphonic acid (70% aq; 1.0 g) produced a rigidpolymer after 3 minutes at room temperature, and polymerization wascompleted by heating to 60° C. for 30 minutes. Water and heptane wereremoved at 75° C. under vacuum.

The resulting porous polymeric material had similar physical propertiesto the product of Example 1.

EXAMPLE 3

The same procedure was used as described in Example 1. 3.0 g ofresorcinol and 7.9 g of glyoxal (40% aq) were employed. The emulsifierwas MIRANOL C2M-SF. CONC (37% aq; 1.2 g) and the emulsion dispersedphase was petroleum ether (60 ml, 100-120 B.Pt). Addition of thecatalyst, p-toluenesulphonic acid (70% aq; 1.0 g) followed by heating to80° C. for 2 hours produced a rigid polymer. The water and petroleumether were removed at 100° C. under vacuum.

The material had a porosity of about 90% by volume and cell sizesfalling within the range 1 to 15 μm.

EXAMPLE 4

The procedure of Example 1 was followed with the exception that5-methylresorcinol in place of resorcinol and the basic catalyst, sodiumcarbonate (20% aq; 2.0 g), in place of the acidic catalyst, phosphoricacid, were employed. A rigid polymer formed within 20 minutes at roomtemperature. Polymerization was completed by heating for 30 minutes at60° C. Water and cyclohexane were removed in a vacuum oven.

The resulting polymeric material had a porosity and other physicalcharacteristics similar to the product of Example 1.

EXAMPLE 5

A two stage procedure was employed to produce a urea-formaldehyde basedporous polymer. A pre-polymer syrup was prepared initially. Formalin(40% aq; 81 g 1.0 mol), sodium acetate (0.4 g) and concentrated ammonia(S.G. 0.88; 0.8 g) were mixed to form a homogeneous solution. Urea (30g; 0.5 mol) was then added slowly, and the mixture heated and stirredslowly to 90° C. for 30 minutes. This temperature was then maintainedfor 2 hours during which time the solution became cloudy. 35 ml of waterwas then distilled out to yield a turbid pre-polymer syrup (70% solids).The pH of the syrup was adjusted to 7.4 with a few drops of 0.5M NaOH tostabilize the product. In the second step this syrup (12.3 g) was mixedwith a surfactant, MIRANOL C2M-SF. CONC (37% aq; 1.4 g), and cyclohexane(160 ml) stirred into the mixture to form a high internal phaseemulsion. Curing of the pre-polymer was then induced by stirring inammonium chloride (40% aq; 1.0 g) and heating for 2 hours at 50° C. Therigid polymer thus formed was dried at 75° C. in a vacuum oven.

The resulting urea-formaldehyde polycondensation material had an overallporosity of 93% by volume and, as shown by scanning electron microscopepictures, an interconnected cellular structure in which the cells had anaverage diameter of approximately 12 μm. The material was prepared inblock form, but could if desired be readily granulated.

EXAMPLE 6

An alternative one stage version of Example 5 is as follows. A solutionof formalin (40%; 16.2 g; 0.20 mol), urea (6.0 g; 0.10 mol) and MIRANOLC2M-SF. CONC (2.5 g) was prepared and solid ammonium chloride (2.0 g)added. Cyclohexane (197 ml) was stirred in slowly to form a highinternal phase emulsion. The emulsion was heated to 50° C. for 30minutes then left overnight at room temperature to produce a rigidpolymer. The polymer was dried as in Example 5.

The resulting material had similar properties to the product of Example5.

EXAMPLE 7

A phenol-formaldehyde porous polymeric material was prepared in atwo-stage process, the first involving the preparation of a pre-polymer.

A mixture of formalin (40% aq; 55 ml; 0.79 mol), phenol (30 g; 0.32 mol)and sodium hydroxide (30% aq; 1.3 ml) was refluxed for one hour,followed by cooling to room temperature. The pH of the resulting mixturewas adjusted to pH 7.4 with a few drops of molar lactic acid and themixture separated into two distinct phases. Water and excessformaldehyde were removed by rotary evaporation to leave a clearpre-polymer syrup.

A high internal phase emulsion was produced by the dropwise addition,with stirring, of heptane (170 ml) to a mixture of pre-polymer (15 g),water (8 ml) and Miranol C2M-SF. CONC surfactant (2.6 g). Curing wasbrought about by the addition of toluene-4-sulphonic acid (70%aq; 4.0 g)followed by heating for 2 hours at 70° C. Drying of the resultingmaterial was carried cut by heating at 100° C. in a vacuum oven.

The resulting phenol formaldehyde polycondensation polymer was recoveredas an opaque solid which was hydrophobic in nature. Mechanically thematerial was very tough. Assessment of the material by scanning electronmicroscopy showed it to consist of an open interconnecting cellularstructure in which the cells had a diameter within the range 0.2 to 7.0μm. The material had an overall porosity of approximately 90% by volume.

EXAMPLE 8

The procedure of Example 7 was repeated employing 3-aminophenol in placeof phenol.

3-aminophenol (6.0 g; 0.055 mol) was dissolved in a solution of sodiumhydroxide (2.4 g; 0.060 mol) in water (1.0 g). The resulting phenoxidesolution was cooled to below 10° C. and then formalin (40% aq; 8.3 g;0.11 mol) was added incrementally to form a pre-polymer syrup. In orderto prevent premature resinification the temperature was kept below 15°C.

An emulsifier, Miranol C2M-SF Conc (37% aq; 2.8 g) was stirred into thepre-polymer syrup followed by petroleum ether (180 ml; 100-120° C. B.P.)to form a high internal phase emulsion. The emulsion was heated to 80°C. for an hour. The resulting polymer was porous and rigid and had cellsizes within the range of approximately 2 to 25 μm and holesinterconnecting the cells having diameters within the range ofapproximately 0.05 to 6 μm.

EXAMPLE 9

A polyvinyl formal porous polymer was prepared by cross-linking apolyvinyl alcohol. Polyvinyl alcohol (9.0 g), formalin (40% aq; 14 g),water (22.3 g) and Miranol C2M-SF. CONC (2.2 g) were mixed at 90° C. toform a viscous solution. Liquid paraffin (240 mls) was added withstirring to form a high internal phase emulsion. An acid catalysthydrochloric acid (10M; 6.2 g) was slowly added with stirring and theresulting mixture was incubated at 60° C. for 8 hours. The resultingporous polymer was washed free of liquid paraffin.

The resulting porous polymer was hydrophilic and in a hydrated state wassoft in texture with elastic properties. On drying the porous polymershowed slight homogeneous shrinkage and an increase in rigidity.

The hydrated polymer material had cell diameters within the range 5 to20 μm and an overall porosity of approximately 90% by volume.

EXAMPLE 10

A mixed polycondensation polymeric material was prepared.

The first stage of Example 7 was followed to yield a clear pre-polymerphenol formaldehyde syrup. 20 parts by weight of this syrup were admixedwith 80 parts by weight of a polyvinyl alcohol-formalin containingviscous solution described in Example 9. A high internal phase emulsionwas prepared from this admixture by adding with stirring liquidparaffin. Acid catalyst, toluene-4-sulphonic acid (70% aq), was added tothe emulsion which was then allowed to cure at 80° C. for 8 hours.

After extracting the liquid paraffin the resulting porous polymericmaterial was tough and rigid in the dry state. The hydrated polymer hadcells of a similar size to the product of Example 9, but was somewhatfirmer and less elastic.

EXAMPLE 11

A melamine-formaldehyde based porous polymer was prepared by a two stepmethod similar to Example 5. Melamine (63 g; 0.5 mol) was added toneutralised (pH 7-7.5) formalin (40% aq; 113 g; 1.5 mol). Ammoniasolution (0.880; 1.3 ml) was added and the mixture stirred and heated toboiling. The resulting homogeneous solution was refluxed for 40 minutes,then concentrated under reduced pressure to give a clear, viscous syrup(70% solids). An aliquot of this syrup (12.2 g) was diluted withglycerol (2.3 g) and Miranol C2M-SF.CONC (1.5 g). Heptane (100 ml) wasstirred in slowly to form a high internal phase emulsion. Phosphoricacid (50% aq; 1.0 g) was mixed in and the catalyzed emulsion heated at70° C. for an hour.

The resulting polymeric material was further heated at 150° C. undervacuum to dry it and complete the cure.

The final polycondensation material was rigid and comprised an opencellular structure. The cells had a diameter within the range 1 to 12μm. The material had an overall porosity of approximately 88% by volume.

EXAMPLE 12

A polycondensation polymeric porous material embodying the presentinvention was prepared using as a starting material a commerciallyavailable epoxy adhesive resin. A xylen solution of the epoxy resin andhardener containing the water-in-oil emulsifier Span 80 was prepared.Water was stirred into the xylene solution in a ratio of water to xylenesolution of 90:10 to form a high internal phase emulsion with water asthe dispersed phase. The emulsion set to a hard rigid porous polymer inabout 12 hours at room temperature. The porous polymer had an overallporosity of about 90% by volume and interconnecting cells havingdiameters within the approximate range of 1 to 30 μm.

EXAMPLE 13

A polyamide based porous cross-linked polymer was prepared by injectinga high internal phase emulsion containing a diamine into an organicphase containing a triacid chloride. Hexamethylene diamine (2.3 g),triethylamine (4.4 g) and Miranol C2M-SF. CONC (37% aq; 1.2 g) weremixed together. Cyclohexane (80 ml) was stirred into this mixture toform an emulsion. A receiving phase consisting of1,3,5-benzenetricarboxylic acid chloride (3.5 g) in toluene (20 ml) wasprepared. The emulsion was introduced into a glass syringe, and thenceextruded into the receiving phase. Polymer was formed when the reagentswere contacted and they were allowed to react for a further hour at roomtemperature. The resulting porous polymer was washed with water andether, and dried under vacuum.

The polyamide (nylon 6,6) material recovered was in the form of threadsand granules as a result of the extrusion approach to its preparation.Mechanically the polycondensation material was found to be tough, butalso rather brittle. Scanning electron microscopy analysis showed thematerial to have an interconnected open cell structure, with the cellshaving a diameter within the range 1 to 10 μm. The dried material had anoverall porosity of approximately 90% by volume.

EXAMPLE 14

The procedure of Example 13 was repeated using in place of thehexamethylene diamine, m-phenylene diamine (2.2 g).

The resulting porous polymer had similar physical properties to those ofExample 13.

EXAMPLE 15

A silicone based porous polymer was prepared by cross-linking a linearsiloxane pre-polymer. Silicone pre-polymer B (J-SIL Silicones (UK), 11.5g) which is a room temperature vulcanizable silicone elastomercomprising silanol capped polysiloxane, SILESTER OS (Monsanto, 8.0 g)which is a polymeric alkyl silicate containing the equivalent of 40%SiO₂, and two surfactants, ARLACEL 987 (a sorbitan mono-oleate having anHLB of 4.3; 1.8 g) and SPAN 85 (a sorbitan monoisostearate having an HLBof 4.3; 1.8 g), were mixed together. The catalyst dibutyl tin dilaurate(0.5 g) was added as the last component of this phase. Water (130 ml)was stirred in by hand to form a high internal phase emulsion over aperiod of 15 minutes. The emulsion was then left to cure for a further30 minutes at room temperature before it became rigid, while remainingflexible. After further curing at room temperature overnight, and dryingat 60° C. in a vacuum oven, a soft porous silicone based polymer wasobtained.

The resulting polysiloxane, silicone based, polymer had an open cellularstructure with the constituent cells having an average diameter of about10 μm. The material was opaque, soft and flexible in nature andexhibited a snappy elastic return. The material had an overall porosityof approximately 80% by volume.

EXAMPLE 16

A proteinaceous porous polymer was prepared by cross-linking amacromolecular structured polyamide bovine serum albumin.

Bovine serum albumin was dissolved in an aqueous phase at aconcentration of 30 wt:%. An oil-in-water emulsion having an internalphase of 86% by volume was formed by the addition with stirring of lightliquid paraffin in the presence of Miranol C2M-SF. CONC (2 g per 100 mlreaction mixture). Aliquots of the high internal phase emulsion weredialysed against 50 wt % gluteraldehyde solution.

The resulting cross-linked polymeric material had an open cellularstructure which allowed the internal oil phase to be removed and thematerial to be washed and dried. On drying a small amount of homogeneousshrinkage occurred. The dried material was self-supporting, hard andbrittle.

Prior to drying the porous material had an overall porosity ofapproximately 86% by volume and comprises interconnected cells havingdiameters within the range 1 to 20 μm.

Tests were performed on each of the above products to show thecross-linked nature of the polycondensation porous materials. Eachproduct was subjected to a series of tests in order to assess itssolubility with respect to a range of solvents. Each test was performedby covering approximately 50mg of the product with 3 to 5 ml of the testsolvent in a test tube and leaving overnight. The effect of the solventon the products after the respective time was noted. Each product wassubjected to a dissolution test in each of: water, toluene, chloroform,dimethylformamide; concentrated (98%) sulphuric acid (H₂ SO₄), acetone,and in some cases m-cresol. The toluene and m-cresol tests involvedheating in a bath held at 80° C. for 6 hours.

By way of comparison equivalent tests were performed on a range ofporous polycondensation materials that were known to be notcross-linked. These materials were prepared by the method disclosed inGB No. 1576228 (AKZO) in which it is an essential feature of thepreparative method disclosed that the resulting polymeric materials arethermoplastic and soluble. Two of the comparative materials tested wereexamples of materials obtained commercially from AKZO and thus made byAKZO.

The comparative materials employed and produced according to the methoddisclosed in GB No. 1576228 were: A. polyethylene; B. polypropylene(commercially available sample); C. polystyrene; D. synthetic butylrubber (70% butadiene content); E. ethylene/acrylic acid salt copolymer(>40% CO₂ Na); F. polycarbonate (from Bisphenol A); G. polyphenyleneoxide; H. nylon 6 (commercially available sample); I. nylon 66; J. nylon11.

The results of the tests are given in the Table below.

    __________________________________________________________________________    Product                                                                            Solvent Tested                                                           Example                                                                            Toluene                                                                            Chloroform                                                                          Water                                                                             DMF H.sub.2 SO.sub.4                                                                  Acetone                                                                            m-Cresol                                     __________________________________________________________________________    1    I    I     I   I   I (sw)                                                                            I    --                                           3    I    I     I   I (sw)                                                                            I (sw)                                                                            I    --                                           4    I    I     I   I   I (sw)                                                                            I    --                                           5    I    I     I   I   I (p/d)                                                                           I    --                                           7    I    I     I   I   I   I    --                                           8    I    I     I   I   I (sw)                                                                            I    --                                           9    I    I (sw)                                                                              I (sw)                                                                            I (sw)                                                                            I (sw)                                                                            I (sw)                                                                             --                                           10   I    I (sw)                                                                              I (sw)                                                                            I (sw)                                                                            I   I    --                                           11   I    I     I   I   I (sw)                                                                            I    --                                           12   I (sw)                                                                             I (sw)                                                                              I   I (sw)                                                                            I (sw)                                                                            I    --                                           13   I    I     I   I   I (sw)                                                                            I    I                                            14   I    I     I   I   I (sw)                                                                            I    I                                            15   I (sw)                                                                             I (sw)                                                                              I   I   I (d)                                                                             I    --                                           16   I    I (sw)                                                                              I   I (sw)                                                                            I (sw)                                                                            I    --                                           A    S    --    --  --  --  --   --                                           B    S    --    --  --  --  --   --                                           C    S    S     --  --  --  S    --                                           D    --   S     --  --  --  --   --                                           E    --   --    S   --  --  --   --                                           F    --   S     --  S   --  --   --                                           G    S    --    --  S   --  --   --                                           H    --   --    --  --  S   --   S                                            I    --   --    --  --  S   --   S                                            J    --   --    --  --  S   --   S                                            __________________________________________________________________________     I: Insoluble                                                                  S: Soluble                                                                    sw: swollen                                                                   p: partially soluble                                                          d: chemically degraded                                                   

As can be seen from the results tabulated above all of the productsembodying the present invention are insoluble in a range of solvents.The very aggressive solvent concentrated sulphuric acid caused in anumber of instances chemical degradation of the materials.

By contrast the range of non-cross-linked samples were readily soluble.

We claim:
 1. A three-dimensional porous polymeric material having a voidspace consisting of a three-dimensional network of cells separated fromeach other by walls and interconnected by holes through said walla, thecells having diameters in the range 100 to 0.5 μm, and the void spacebeing in the range 75 to 98% of the total volume of the polymericmaterial, wherein the polymeric material is a cross-linkedpolycondensation polymeric material, said polymeric material beingformed by a bulk condensation polymerization and condensationcross-linking process occurring in the continuous phase of an emulsionwhich phase contains polymerizable precursor materials for saidpolymeric material, the emulsion having an internal phase comprising 75to 98 volume % of said emulsion material and consisting of globuleshaving dimensions in the range of 100 to 0.5 μm.
 2. A polymeric materialaccording to claim 1 wherein the cross-linked polycondensation polymericmaterial is derived from monomers and/or pre-polymers or mixturesthereof having at least two different reactive groups.
 3. A polymericmaterial according to claim 1 wherein the cross-linked polycondensationpolymeric material is derived from at least two types of monomers orpre-polymers.
 4. A polymeric material according to claim 1 wherein thecross-linked polycondensation polymeric material is derived from apolycondensation polymer material.
 5. A polymeric material according toclaim 1 having an overall density of less than 0.25 g/cm³.
 6. Apolymeric material according to claim 1 having cell sizes within therange 50 to 0.5 μm.
 7. A polymeric material according to claim 1 whereinthe holes in the walls of the cells lie in the range of 0.2 to 0.05 porediameter.
 8. A polymeric material according to claim 1 wherein thecross-linked polycondensation material is selected from the groupcomprising the polycondensation products between urea and aldehydes, thepolycondensation products between phenols and aldehydes, thepolycondensation products between resorcinols and aldehydes, polyvinylformals, polyesters, polyamides, polyacetales, polyurethanes,polysiloxanes, polyimides, polybenzimidazoles, polyethers,polythioethers, polyketals, polyether sulphones and polyether ketonesand mixtures thereof.